Electrode for semiconductor devices



Dec 14, 1954 J. P. STELMAK ELECTRODE FOR SEUICONDUCTOR DEVICES Filed NOV. 16. 1949 :inventor Imm P. STELMAK tomen United States Patent O ELECTRODE FOR SEMICONDUCTOR DEVICES John P. Stelmak, Forest Hills, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application November 16, 1949, Serial No. 127,615

S Claims. (Cl. 317-235) This invention relates lo semiconductor devices and particularly to multi-electrode semi-conductor amplifiers and oscillators.

A semi-conductor device or transistor which may be used as an amplifier or oscillator, generally includes a semiconducting crystal provided with a low-resistance, largearea electrode usually called the base electrode and with two high-resistance, small-area electrodes which are cornmonly designated emitter and collector electrodes. The emitter and collector electrodes usually are point electrodes which are in rectifying contact with the semi-conducting crystal. These two point electrodes are closely spaced from each other and their distance is of the order of a few mils and many amount to less than one mil. The gain, the power output and the high frequency performance of such a semiconductor amplifier are greatly improved by a closer spacing of the emitter and collector electrodes. However. such close spacing of the rectifying electrodes presents appreciable mechanical difficulties and furthermore short circuits may occur between the emitter and collector electrodes when they are spaced one mil or less.

It is an object of the present invention, therefore, to provide an improved multi-electrode semi-conductor amplier or oscillator having an electrode structure which permits closer spacing of certain electrodes thereby to provide high gain while preventing short circuiting of said electrodes.

A further object of the invention is to provide improved rectifying electrodes, that is, emitter and collector electrodes. for a transistor which will facilitate the positioning of the electrodes on the semi-conducting crystal with a redelermined small distance between the electrodes w ich may be of the order of one mil, for purposes above stated.

A semi-conductor device in accordance with the present invention com rises a semi-conducting body and two electrodes in recti ying contact with the body. The two rectifying electrodes are s aced from each other and insulated by a relatively thin ayer or film of insulating material which is disposed between the electrodes. Thus, the two electrodes may consist of wires having pointed ends, each wire being coated with an insulating layer. ln this case, the spacing of the electrodes is determined by the thickness of the insulatin coating. Alternatively, one of the electrodes may cons st of a pointed wire wh le the second electrode may be a tube enclosing the first electrode and having a tapered end portion contacting the crystal. An insulating s eeve spaces the two electrodes and prevents short circuiting thereof.

The novel features that are considered characteristic of this invention are set forth with particularity in the apndcd claims. The invention itself, however. both as to tts organization and method of operation, as well as additional objects and advantages thereof. will best be understood from the following description when read in connection with the accompanying drawing, in which:

Figure l is a side elevational view, with parts broken tway, of a three-electrode semi-conductor device embodyng the invention;

Figure 2 is a side elevational view, with parts broken way, of a modied transistor in accordance with the in- 'entiom and Figure 3 ls a top plan view of the transistor Figure 2.

Referring now to the drawing in which like components ave been designated by the same reference numerals trottghout the figures, and particularly to Figure l, there illustrated a semi-conductor device embodying the res- 1t inventlon which may be used as an amplifier, oscil ator 2,697,189 Patented Dec. 14, 1954 ice or the like. The device comprises a block or body 10 of semi-conducting material consisting, for example, essentially of a chemical element having semi-conducting properties such as germanium, silicon, boron, tellurium, or selenium containing a small but sufficient number of atomic impurity centers or lattice imperfections as com monly employed for best results in crystal rectifiers. Germanium is the perferred material for body 10 and may be prepared so as to be an electronic N-type semi-conducting crystal as is well known. The top surface of semi-conducting body 10 may be polished and etched as is conventional. lt is also feasible to utilize the germanium block from a commercial high-back voltage germanium rectifier such as the type lN34.

Electrode 11 makes a large-area. low-resistance contact with body 10 and may be used as the base electrode of a semiconductor amplifier. Electrode ll may consist of any suitable metal such as copper which may, for example, be soldered or sweated to body 10. Electrodes 12 and 14 are in rectifying contact with body l0. Electrode 12 is the collector electrode and has a point contact with body 10. Thus, collector electrode 12 may consist of a wire of tung sten or Phosphor bronze which may have a diameter of 5 mils or less. Collector electrode 12 preferably is provided with a conical tip 13 as shown to provide substantially a point contact with the surface of body 10. Electrode 14 is the emitter electrode preferably consisting of a metallic tube or sleeve surrounding collector electrode 12. Emitter electrode 14 may be made of the same metal of which electrode l2 consists. Emitter electrode 14 is provided with a tapered end portion 15 having a sharp edge in contact with body 10. Thus, emitter electrode 12 also has essentially a point contact or a small-area contact with body 10. The edge of emitter electrode 14 in contact with the surface of body 10 may be circular, semi-circular or a smaller portion of a circle.

ln accordance with the present invention, collector electrode 12 is provided with insulating layer or film 16 of predetermined fixed thickness which s aces electrodes 12 and 14 as shown. insulating layer 16 oes not extend over conical end portion 13 of collector electrode 12 or over the tapered end portion l5 of emitter electrode 14. Insulatin layer 16 may, for example, consist of a suitable film o enamel or of formex or collector electrode l2 which is conventionally employed to insulate line wire such as used for the windings of electromagnets. Alternatively, wire l2 may be sprayed with unpolarized Lucite to provide an insulating film of the desired thickness. instead of applying insulating layer 16 by spraying it on wire 12 an insulating sleeve may be provided of a suitable insulating material. This ma for example. be achieved by coating wire 12 with a suita le grease and spra ing enamel or Lucite over the grease. The advantage o such an arrangement is that insulating sleeve 16 may be moved with respect to wire 12.

lnsulatin layer 16 thus serves the purpose of spacing electrodes 2 and 14 from each other and locating them on the surface of bod 10. lt is still possible. however, to move one electrode with respect to the other longitudinally. The gap between conical point 13 and tapered end portion 15 may be ap roximately 2 mils.

A modifi semiconductor device in accordance with the invention is illustrated in Figures 2 and 3. Semi-conducting body 10 is again provided with base electrode 11 in the manner previously described. Two electrodes 20 and 21 are provided which are point electrodes in rectifying contact with the surface of body l0. Electrodes 20, 21 are the emitter art-i collector electrodes and may consist of wires of tungsten or Phosphor bronze having a diameter of 5 to l0 mils. Preferably each wire is coated with a film 22 consisting of an insulating material as reviously explained. Each wire 20 and 21 is then provi ed with a ch sel point indicated at 23 so that the two wires are spaced from each other b twice the thickness of film 22, the two chisel points 23. 3 being disposed in opposed relation. The thus resulting two point electrodes ma be s aced apart approximately one mil depending on t e thic ness of film 2 The two wires 20 and 21 are secured to aceramic or plastic support 2S which is provided above bod 10 as clearly shown ln Figure 2. One extremity of eaeii wire 20 and 2l may be secured to support 25 by suitable means such as rivets 26. The two wires extend parallel to each other from their chisel points 23 through an opening 27 in support 25. Opening 27,is sutficiently large to allow free movement of the wires 20, 21 therethrough. The intermediate portions of the wires are curved as indicated at 3l) and 3l to provide a spring action when support 25 is pressed against body l0 to provide the desired contact pressure between chisel points 23 and body l0. The curved portions 30, 3l may consist of two loops 32 and 33 extendmg approximately at right angles to each other as clearly shown in Figures 2 and 3.

lt is to be understood that it is only necessary to provide one of the wires 20 or 21 with an insulating film 22. Alternatively, one or both of the wires 20 and 21 may be provided with an insulating sleeve 22. The construction of Figures 2 and 3 will considerably facilitate the positioning of the wires and their spacing which is determined by the thickness of film 22.

There has thus been disclosed an improved semi-conductor device having emitter and collector electrodes which are spaced by an insulating member or hlm which may be sprayed on one or both of the electrodes. This insulating tilm will prevent short circuitittg between the emitter and collector electrodes and will consequently permit a considerably closer spacing of the electrodes thereby to improve the gain, the power output and the high frequency performance of thedevicc.

What is claimed is:

l. A semi-conductor device comprising a semi-conducting body, an insulating supporting member spaced from said body and having an opening, a pair of electrodeseach consisting ot' a lamentary conductor having one extremity secured to said member, the other extremity of each oi' said conductors having a sha point in contact with said body, a further electrode in l Haw-resistance contact with said body, and an insulating llm covering one of said conductors with the exception of its point, said conductors extending parallel to each other and spaced by said lm from said points through the opening in said member and having each a curved intermediate por"- ion to provide a spring action when said member is pressed toward said body, said supporting member being disposed between said point and said curved ortion of each of said conductors.

2. A semt-conductor device comprising a semi-conducting body, an insulating supporting member spaced from said body and having an aperture, a pair of electrodes. each consisting of a llamentary metallic conductor having one extremity secured to a portion of said member. said portions betng disposed opposite said aperture, the other extremity of each of said conductors having a chisel point in contact with said body, a further electrode in low-resistance contact with said body, and an insulating layer covering each of said conductors with the exception of said chisel points` said conductors extending parallel to each other and spaced by said layers from sid chisel points through the aperture in said member and having each a curved intermediate portion to provide a spring action when said member is pressed toward said body to provide a desired contact pressure between said. bod and said chisel points, said supporting member being dtsposed between said point and said curved portion of each of said conductors and in close proximity to the surface of -said body contacted by said conductors.

3. A semi-conductor device comprising a semi-conducting body, an insulating support member spaced from said body and having an opening, a pair of electrodes, each consisting of a wire having one extremity secured to opposite portions of said support with respect to said opening, the other extremity of each of said wires having a chisel point in contact with said bod said chisel points being disposed in opposed relation, a urther electrode in low-resistance contact .with said body, and an insulating film covering cach of said wires with the exception of said chisel points, said wires extending parallel to each other and spaced by said films from said chisel points through the opening in said member and having each an intermediate portion with two loops extending approximately at right angles to each other to provide a spring action when said member is pressed toward said body to provide :t predetermined con tact pressure between said body and said wires, said sup port member being positioned between said point and said loops of each of said conductors and in close proximity to both said points of said conductors and to the surface of said body contacted by said points whereby close spacing between said conductors is achieved and maintained andl wherby said predetermined Contact pressure is maintaine 4. A semi-conductor device comprising a semi-conducting body, an insulating support member spaced from said body and having an opening, a pair of small area electrodes insulated from each other and extending through said opening, said electrodes being in rectifying contact with said body and each having a curved intermediate portion. said insulating support member being positioned between said body and said curved portion of said electrodes, and a further electrode in low resistance Contact with said body.

5. A semi-conductor device comprising a semi-conducting body, a insulating disk support member spaced from said body and having an opening, a pair of small area filamentary `electrodes extending through said opening and in rectifying contact with said body, cach of said electrodes having a curved intermediate portion to provide a spring action. an insulating film separating said electrodes, said insulating support member being positioned between said body and said curved portion of said electrodes. and a further electrode in low resistance Contact with said body.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,900,018 Lilienfeld Mar. 7. i933 2.d!i6,776 Barney Nov. l. |949 2.6l5.965 Amico Oct. 28, 1952 

